Honest and harsh aren’t the same setting. You can tell the truth without turning the brightness all the way up.

Harshness often travels disguised as honesty, since both involve saying something unwelcome. The difference is what the extra force is for, and usually it is for the speaker: a little satisfaction, a little release, nothing the listener needed. Remove all of it and the truth stays exactly as true. What changes is whether it can be heard.

Say the hard thing at the lowest setting that still delivers it. Cut the adjectives, the saved up examples, and the summary of past offences. If it feels less satisfying to say, you are probably doing it right.